(1) Field Of the Invention
The present invention relates to a structure of telescopic steering apparatus applicable to a vehicle, in which a steering shaft of a steering column onto which a steering wheel is fixed is telescopically movable in an axial direction of the steering shaft.
(2) Background Of the Art
Recent automotive vehicles have adopted tilt-type and/or telescope-type steering apparata in order to assure adjustments of optimum driving positions for vehicle drivers.
In the telescope-type (telescopic) steering apparata, steering shafts are telescopically movable in steering column jackets within constant limits of movements.
The steering shaft in the telescopic steering apparatus includes a cylindrical shaft and shaft body engaged together via a spline. The steering wheel is axially fixed to a free end of the shaft body. The shaft body can manually or electrically be inserted into or separated from the cylindrical shaft. In the former manually operable type shaft body, a lock portion for fixing both shaft body and cylindrical shaft members together is additionally installed.
On the other hand, in the tilt-type steering apparata, an upper end of the steering column jacket is supported on a clamp fixed to a vehicle body via a movable bracket with a tit hinge as a center so that the steering wheel can be pivoted in the upward and downward directions.
In addition, combination-type steering apparata of both tilt-type (tiltable) and telescope-type structures have recently been adopted in many automotive vehicles.
However, since in the previously proposed telescopic steering apparata the cylindrical shaft is axially fitted to the shaft body in the axial direction, a rigidity of the steering shaft tends to be reduced if the axis body is extended from the cylindrical shaft at its maximum length.
In addition, when the shaft body is drawn at its maximum into the cylindrical shaft after the maximum extension of the shaft body from the cylindrical shaft, an upper end of an upper jacket of the steering column jacket often collides violently with an upper end of an inner tube so that an abnormal sound of shock is produced. The telescopic steering shaft may be damaged and vehicle occupants feel unpleasantly.
To cope with such collisions, nonmetallic stoppers are installed on the upper end portion of the upper jacket and upper tube of the column jacket, respectively, so that the collision of both members can be damped.
However, since such kinds of stoppers are made of plastically deformable members such as synthetic resins, they are susceptible to be damaged. Hence, the structures of the whole stoppers tend to become complex, large-sized, and heavy in weight to endure a certain magnitude of shock upon collision. Consequently, the manufacturing cost becomes increased.